Typical semiconductor pressure sensors use solid state sensing elements that are not compatible with liquids. When the pressure of a liquid is being sensed, these devices require complicated packaging schemes to mount the sensing element and to protect that element from the fluid passing through the pressure sensor package.
A packaging scheme is known for a pressure gauge such that the pressure gauge can be used to detect the pressure of either a liquid or a gas. The package of this pressure gauge includes a solid state pressure sensing element and elastomeric seals. The pressure gauge detects any change in pressure of a fluid. In past designs, at least one of the elastomeric seals is conductive so as to connect signals from the solid state pressure sensing element to electrical leads that exit the housing of the pressure gauge. This type of pressure gauge is shown in U.S. Pat. No. 5,184,107 issued to Dean J. Maurer on Feb. 2, 1993. Also, the pressure sensor described in U.S. Pat. No. 6,826,966 issued to Karbassi et al on Dec. 7, 2004 integrates a pressure sensing element and a restriction into a low-cost, highly-manufacturable sensor package. The Karbassi et al packaging arrangement exposes the pressure sensing element to the gas or fluid flow but protects the susceptible regions of the pressure sensing element from the gas or fluid without the need for other protective devices.
Industry has been experiencing a problem wherein conductive elastomeric seals cause shorting when and if they wrap over the edge of the die. When a conductive elastomeric seal wraps around the edge of a die associated with a pressure sensor, it can short out the Wheatstone bridge or other electronic circuitry located on the sensor package.
Pressure sensors packaged using the elastomeric seals have an inherent problem with the seal that is conductive if perfect alignment is not held when the package is snapped together and the seals are compressed because elastomeric seals are impregnated with thin silver strips. The strips themselves do not necessarily contact each other in the seals, but they do extend and contact the metallization on the die they are used with and create contact through the seal with the sensor package. Due to manufacturing tolerances, the silicon pressure die must be slightly smaller then the package housing in order for the silicon die to fit into the housing. When compressed, the conductive seal can wrap over the edge of the die and short to N type epi causing a sensor error or failure. This problem is more pronounced for sensing higher pressures, but can exist in any pressure range.
What is needed is a way to overcome the problem of shorting because of the use of conductive elastomeric seals for making contact inside the pressure sensor packages.